Postural change and straining induced by distension of the rectum, vagina and urinary bladder of decerebrate dogs.

In decerebrate dogs, stimulation of pelvic afferent fibres and distension of the rectum, vagina and urinary bladder brought about a sustained postural change and rhythmic abdominal compression. The posture, which resulted from flexion of the back and stifle joints, extension of the hip joints and lifting of the tail, was rhythmically intensified with the abdominal compression. The sustained and rhythmic postural changes are similar to those observed in conscious dogs during defaecation. Intratracheal pressure increased with the abdominal compression. Nervous outflow to the muscles of the glottis, diaphragm, abdominal wall, tail and rear legs changed as would be expected from both the postural changes and the increases in intratracheal and intra-abdominal pressure. Nervous outflow to the external sphincter muscles of the anus and urethra increased simultaneously with both kinds of postural change; however, the increased outflow to the anus was suppressed when defaecation was initiated, and the outflow to the urethra was suppressed when micturition was initiated. In about one-third of the dogs, decreases in the outflow of the pelvic rectal branch and slight increases in the outflow of the vesical branch occurred synchronously with the abdominal compression. These results show that postural change and straining for defaecation, micturition and parturition are reflexly organized by the lower brainstem and the spinal cord.